Field of the Invention
This invention relates to reciprocating fluid power cylinders of the hydraulic or pneumatic type wherein it is desirable to prevent relative rotation between the piston and the cylinder.
In a variety of mechanical systems utilizing a hydraulic or pneumatic piston of a power cylinder to achieve reciprocal motion, for example, machine tools, fluid actuated controls for aircraft and other vehicles, and pumps, it is often desirable to prevent relative rotation between the piston rod and the cylinder barrel.
A first example of a prior art device of this type wherein relative rotation between the piston rod and cylinder barrel is prevented employs a non-circular guide rod having a square or splined configuration, for example, over which the piston and piston rod slide. In order to prevent this assembly from rotating relative to the cylinder barrel, the non-circular guide rod is rigidly fastened to the cylinder barrel or cylinder end cap by means of a threaded connection, cooperating internal and external splines, or a locking pin which can be indexed to various positions about the axis of the cylinder barrel. A difficulty with this type of prior art device is that angular adjustments are made difficult due to the necessity for axial tightening of the guide rod in the case of a threaded connection, and the fact that adjustment can only be made by an integral number of teeth in the case of a splined connected or an indexable pin. Another problem with this type of device is that if there is any angularity in the connection between the guide rod and end cap, the piston will be forced off to one side so that it binds as it reciprocates.
In another prior art device, the splined guide rod is drawn down into a cap made of a soft material which prevents it from rotating about its axis. The splines make slight indentations inside the cap, however, and if an angular adjustment is attempted which is not an integral number of teeth, the spline tends to fall back into one of the ridges which it had previously formed in the cap.
A further type of prior art fluid power cylinder having a non-rotating feature employs a plurality of auxiliary guide rods which extend parallel to the center guide rod. The drawback to this design is that it requires the use of additional seals to prevent fluid leakage from the cylinder. Furthermore, the presence of the auxiliary shafts reduces the working area of the piston.
Another prior art example of non-rotating fluid cylinders employs a piston rod having a non-circular configuration with one or more flat sides slidably engaging complementary flat surfaces in the bearing for the piston rod. The flat surfaces are difficult to seal, however, so that fluid leakage becomes a problem.